1. Field of the Invention
The present invention relates to a parity storing method and an error block recovering method in an external storage subsystem, and more particularly to a parity storing method and an error block recovering method in an external storage subsystem, which improve recovering multiple error blocks.
2. Description of the Related Art
RAID (redundant array of independent disks) combines multiple disk drives having a plurality of storage blocks into a single logical disk drive, thereby providing large storage capacity, improving accessing speed, etc.
There are various types of RAID, for example, RAID level-0 through RAID level-5, which are classified according to an array structure and an array characteristic. In the RAID level-4 and the RAID level-5, several storage blocks are grouped into a striping block according to predetermined rule, and a parity block is provided for storing therein parity information based on a data group stored in each striping block, thereby allowing an error block to be recovered.
Recently, as the amount of data to be processed has increased, a plurality of error blocks can occur due to a disk failure, a reading error, etc. However, in the case of the RAID level-4 and the RAID level-5, the number of recoverable error blocks is limited to only one per one parity group in the same striping block.
To overcome the above shortcoming of the RAID level-4 and RAID level-5, various parity storing methods have been proposed, such as RAID level-6 using a Reed-Solomon code, an EVENODD method using a row parity group and a diagonal parity group, etc. However, in these proposed parity storing methods, it is impossible to recover three or more error blocks per one parity group.